An α-particle model for 16O: is there a new four-body scale?

The 16O nucleus is modelled as a system of four α-particles. It is shown that a Hamiltonian that includes established two- and three-body forces reproducing the α-α phase shifts, the 8Be resonance, and the first and second 0+ states of 12C overbinds the 16O nucleus. To rectify this a novel four-body force is introduced, which then leads to a good agreement with the low-lying experimental spectrum of 16O. (author)